IL-2 is effective treatment for a significant minority of patients with melanoma or renal cell cancer. Treatment of other cancers has been much less successful, and treatment of all patients can be limited by severe systemic toxicity particularly at high doses of IL-2. The encapsulation of IL-2 in liposomes may permit treatment of patients at currently effective doses with less toxicity, or it may lead to improved efficacy by increasing the dose of IL-2 that can be administered safely. It is also possible that the accumulation of liposomal IL-2 in certain organs will lead to more effective therapy of metastases to these sites. We have initiated a phase Ia/Ib study of liposome-encapsulated IL-2 in patients with advanced cancer. Liposomal IL-2 is given by 30 min. IV infusion once during week one, three times during week two and five times during week three. Responding patients are eligible for additional therapy. In addition to response to therapy, patients are monitored for toxicity and for immunologic changes secondary to treatment. Twenty-two patients have been treated at the following dose levels: 1X10(6) u2/m2; 3x10(6) u2/m2; 4.5x10(6)u2/m2 and 6x10(6) u2/m2. Dose-limiting toxicity has not been observed and accrual of patients continues at higher dose levels. There have been one partial response and two minor responses. Increases in NK activity and serum soluble IL-2 receptor levels have been noted at doses of equal to or greater than 4.5x10(6) u2/m2.